Gateway Apparatus, Communication System, and Delay Measurement Method

1. A gateway apparatus comprising: a packet transmitting unit which transmits to a counter apparatus a first packet that coincides with a packet transmitted immediately before reception of a delay measurement instruction for an IP (Internet Protocol) network between the gateway apparatus and the counter apparatus connected via the IP network; a duplicate packet detecting unit which detects a second packet that is transmitted from the counter apparatus in response to reception of the first packet and coincides with a packet transmitted immediately before reception of the first packet; and a time measuring unit which measures a time until said duplicate packet detecting unit detects the second packet after said packet transmitting unit transmits the first packet.

2. An apparatus according to claim 1 , further comprising a packet holding unit which temporarily holds a packet transmitted from said packet transmitting unit, wherein said packet transmitting unit extracts a packet held by said packet holding unit upon reception of the delay measurement instruction, and transmits the packet as the first packet.

3. An apparatus according to claim 1 , wherein said counter apparatus comprises a second duplicate packet detecting unit for detecting the first packet transmitted to the counter apparatus, and a second packet transmitting unit for transmitting to the gateway apparatus the second packet which coincides with a packet transmitted immediately before the first packet is detected.

4. An apparatus according to claim 3 , further comprising a duplicate creation instructing unit which is activated upon reception of the delay measurement instruction, and instructs said packet transmitting unit to transmit the first packet.

5. An apparatus according to claim 4 , wherein said counter apparatus comprises a second duplicate creation instructing unit, and said second duplicate packet detecting unit activates said second duplicate creation instructing unit and causes said second duplicate creation instructing unit to instruct the second packet transmitting unit to transmit the second packet, wherein when said second duplicate creation instructing unit is active upon detection of a packet, causes said time measuring unit to measure a time.

6. An apparatus according to claim 1 , wherein said time measuring unit measures a time to measure a round trip delay value of a route through which an RTP stream serving as a sequence of data transmitted using RTP (Real time Transport Protocol) passes.

7. An apparatus according to claim 6 , wherein said time measuring unit measures a round trip delay value in the gateway apparatus—the counter apparatus—the gateway apparatus when the RTP stream exists between the gateway apparatus and the counter apparatus.

8. An apparatus according to claim 6 , wherein the first packet and the second packet include an RTP packet.

9. A communication system comprising a first gateway apparatus and a second gateway apparatus which are connected to each other via an IP (Internet Protocol) network, said first gateway apparatus comprising; a first packet transmitting unit which transmits to said second gateway apparatus a first packet that coincides with a packet transmitted immediately before reception of a delay measurement instruction for the IP network between said first gateway apparatus and said second gateway apparatus; a first duplicate packet detecting unit which detects a second packet that is transmitted from said second gateway apparatus in response to reception of the first packet and coincides with a packet transmitted immediately before reception of the first packet; and a time measuring unit which measures a time until said first duplicate packet detecting unit detects the second packet after said first packet transmitting unit transmits the first packet.

10. A system according to claim 9 , wherein said first gateway apparatus further comprises a first packet holding unit which temporarily holds a packet transmitted from said first packet transmitting unit, and said first packet transmitting unit extracts a packet held by said first packet holding unit upon reception of the delay measurement instruction, and transmits the packet as the first packet.

11. A system according to claim 9 , wherein said second gateway apparatus comprises a second duplicate packet detecting unit which detects the first packet from said first gateway apparatus, and a second packet transmitting unit which transmits to said first gateway apparatus the second packet that coincides with a packet transmitted immediately before the first packet is detected.

12. A system according to claim 11 , wherein said second gateway apparatus comprises a second packet holding unit which temporarily holds a packet transmitted from said second packet transmitting unit, and said second packet transmitting unit extracts a packet which is held by said second packet holding unit upon detection of the first packet, and transmits the packet as the second packet.

13. A system according to claim 9 , wherein said time measuring unit measures a time to measure a round trip delay value of a route through which an RTP stream serving as a sequence of data transmitted using RTP (Real time Transport Protocol) passes.

14. A system according to claim 13 , wherein said time measuring unit measures a round trip delay value in said first gateway apparatus—said second gate apparatus—said first gateway apparatus when the RIP stream exists between said first gateway apparatus and said second gateway apparatus.

15. A system according to claim 13 , wherein the first packet and the second packet include an RTP packet.

16. A delay measurement method comprising the steps of: causing a first gateway apparatus to transmit to a second gateway apparatus a first packet that coincides with a packet transmitted immediately before reception of a delay measurement instruction for an IP (Internet Protocol) network between the first gateway apparatus and the second gateway apparatus; causing the second gateway apparatus to detect a first packet from the first gateway apparatus; causing the second gateway apparatus to transmit to the first gateway apparatus a second packet that coincides with a packet transmitted immediately before the first packet is detected; causing the first gateway apparatus to detect the second packet from the second gateway apparatus; and causing the first gateway apparatus to measure a time until the second packet is detected after the first packet is transmitted.

17. A method according to claim 16 , further comprising the step of causing the first gateway apparatus and the second gateway apparatus to temporarily hold transmitted packets, wherein in the step of transmitting the first packet, a packet held upon reception of the delay measurement instruction is transmitted as the first packet, and in the step of transmitting the second packet, a packet held upon detection of the first packet is transmitted as the second packet.

18. A method according to claim 16 , wherein in the measurement step, a time is measured to measure a round trip delay value of a route through which an RTP stream serving as a sequence of data transmitted using RTP (Real time Transport Protocol) passes.

19. A method according to claim 18 , wherein in the measurement step, a round trip delay value in the first gateway apparatus—the second gateway apparatus—the first gateway apparatus is measured when the RTP stream exists between the first gateway apparatus and the second gateway apparatus.

20. A method according to claim 18 , wherein in the steps of transmitting the first packet and the second packet, the first packet and the second packet include an RTP packet.

21. A recording medium which records a program for causing a computer that forms a gateway apparatus connected to a counter apparatus via an IP (Internet Protocol) network to execute a process of transmitting to the counter apparatus a first packet that coincides with a packet transmitted immediately before reception of a delay measurement instruction for the IP network between the gateway apparatus and the counter apparatus; a process of detecting a second packet that is transmitted from the counter apparatus in response to reception of the first packet and coincides with a packet transmitted immediately before reception of the first packet; and a process of measuring a time until the second packet is detected after the first packet is transmitted.